Selective connection of trunk lines



June 5, 1923. 1,457,338

L. D. BARRows ET Al.

SELECTIVE CGNNECTION OF TRUNK LINES Filed April l, 1919 Lul Patented June 5, 1923.

UNITED sr'rss 'i' Y" Vir 'n NEW YORK.'

To all whom 'it may concern:

Be it known that we, LEoN D. BAnRows and LEO H. DARRoW, residing at New York,- win the county of New York and State of'New substations to a common line tothe exclusion of other stations. An instance of this occurs in systems in which a particularsubstation of a-group is given sole useof a trunk line leading to a central station during connection therewith. By the 'present invention this individual connection is brought about when the subscriber atanysubstation removes the receiver from its'hook, the normal condition being automatically restored upon the hanging up of thereceiver.

The accompanying drawing is a diagrammatical representation of the more essential parts of a system arranged inaccordance with one embodiment of this invention.

To a trunk line L leading from a central or other distant station, and connected to battery-B therea't, are joined by leads L1 a Vplurality of substations of which the a paratus of but one is illustrated at A. ach substation line is' provided with. relays R and R1 which are individual thereto. The conductors L1. of each. substation, are shown in the present instance, as being fnormally connected through the back contacts 10 of krelaysR, respectively, and the winding of retardation coil R2 tobattery B1. The relays R1 are shown as connected in series with the substation-'line leads L1. Each relay R is connectedk to thel front contact of its associated relay R1 and through its own back contact 11 and the back contact of a'master relay R3 and conductor 23 to the negative ,side of battery B2. The winding ofthe master relay R2 is common tothe group of s, R relays and is connected to the armatures of all of said relays, and through return conductor 23 lto the negative side of battery B2.

Conductor 21 connectsthe-armatures of re-.

la s R1 to the positive side of batteryB2.

pon the initiation of acall from any of the substations,` the relay R1 individual thereto is operated, said relay being in series with leads l5 and, 1.6, windings of -retarda` Application filed April 1,

LEON BARROWS AND LEO H. DARROW, OF NEW YORK, N. Y., ASSIGNORSTO Y AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF SELECTIVE CONNECTION 0F TRUNK LINES.

1919. SerialNo. 286,670.

tion coil R2 and battery B1. The operation of relay R1 vcloses its contact, and causes the operation of its associated relay R by a path fromthe positive side ofsbattery B2, conductor 241, armatures and contact-of relay R1 conductor 22, winding of connection varying relay R and itsback-contact 11, conductor 12, back contact of master relay R3,

conductor 23 to negative sidelof-battery B2.

The operation of relay R disconnects 'fconduc- -tors L1 from the .back contacts of relay Rand also from conductors 15 and 16, and transfers said conductors L1 to the front contacts of relay R, and thence tothetrunk L, thus coinpleting a circuit Afrom the substation to the distant or central oiiice battery. The operatron of relay R also breaks contact V11 previously closing contact 13. The closing of this latter contact connects th'e winding of master relay R3 in series with the winding of relay R, thus operating relay R3, opening its back contact and closing its 'front contact. Thelv opening of the backcontact results in disconnecting conductor 12, and therefore the windings of all relays R',except the one already operated, from,y battery;` B2, and

therefore prevents their operation as long as relay R,3 maintains its operated position. The closing of the front contact of relay R3 provides a4 locking circuit from positive side of battery B2 tthrough the back Contact, armature and winding of relay R4, conductor 24, front contact and armatureof relay R3, conductor 23 to the negative side of battery B72. The back contact of relay R1 being in series with its operating winding re- ,sults in a buzzer action or alternate open-` ing and closing of its front contact-25. This As has been stated,'a'second'substation at.-k

tempting to obtain access to the trunk .isy Yprevented by the fact that, `although-its relay R1 may operate, the associated relay R will not, because the path to battery B2over conductor l2,which provides for the operation of the last-mentioned relay is openV at j.Contact v11 and making Contact 1 3.

theback l,Contact lof master relay R3. The first :substation to gain access to the trunk L therefore is insured privacy and exclusive use thereof `until `its vrelays R and R1 and master ,lrelaylis are restored to normal by the opening of the circuit at the substation, Which occurs .vhen the receiver is returned to its hook. y y

The details of this circuit may now be more clearly and sufficiently understood. from the following description of its opernation;

Assuming the subscriber A to have taken :the receiver from :its hook for the purpose of conversingvfover the -trunk iL, ya current path is provided fromy said substation, talking conductor L1, through Winding of relay R1, :outer back yContact 10 of relay R, conductor '15, 1left-hand Winding of retardation coil FR?, conductor 19130 negative side of battery #BH-thence :back by Way oi conductor 20, right-hand Winding of said retardation coil,

lconductor 1G.r lmiddle back contact oit relayV R :and second lead Ll to substation.

This

- circuit causes the operation vof relay R1,

ywhich attracts its armature and closes its iront contact, thus providing for the energization Aoi relay R by'means of a current path from the positive side of lbattery B2, conductor'l21, .armature and iront contact of relay 'Rl, conductor 22, winding and back ycontact 11 of relay R, conductor 12, back contact and .armature of master relay R3, conductor 23 t0 lnegative side of-battery B2. Upon the .energizationof relay R its back .contacts l0 are opened and the armatures of said relay make connection With the iront contacts, .thus connecting leads L through ,the :armatures lot rela;v R .and its trent vcontacts to the trunk `L-. This completes :the talking connection from Ithe substation kthrough to the central or distant oiiice. The .energization of relay R also causes it to attract kits left-'hand armature, breaking When `such .contact is established, a current path is providedfrom positive side of battery B2, conductor'fl, armature and contact of relay R1, lconductor 22, Winding, Contact 13 fandlarmature of relay R, conductor 14,

:Windi-ngof .master yrelay R3 and Vover con- .ductor'23 to `negative side of battery B2.,

thus energizing master relay 'R3 and maintaining lthe operation of relay R associated l' `with v,the substation line Which is kin use.

The energization of relay R3 causes it to attract Yits armature, Vbreaking its connec- 'ftionfaby Way of its back contact with con- ,.Clllctor y12 --and making connection by Way of .its @front .contact lwith vconductor 24. This-provides a lockingcircuit vfor master relay Rrbyapath from positive battery B2,

'through the back cont-act, armature and 4Windngof .relay -R .conductor 24C, front contactand` armature of relay R3, and over Vconductor 23 t0 negativeside of battery B2.

The opening of the back contactof master relay R2 makes it impossible for other substations .-to gain access to the trunk, due to the fact that relays Bihave Ano path to battery B2, thus preventing 'the operation of relays R, and subsequent connection of a second substation line to the trunk L. The closing of the front Contact of relay R3 results in the .operation and subsequent buzzing oi relay RL which, by means of the altei-nate opening andclosingo'f its Vfrontl con tact, introduces a lbusy Itone over conductors 17 and 18, thence overconductors15-and 16 which are individual to each substation. rilhe removal of the receiver from its #hook at any of the other s ubstations will ener- :gizethe associated relay R1 individual to that line, but, as pointed outabcve, this :will not vresult in the operationy of the associated relayR. The 'busy tone on leads 15 and 16, however, `Will be 'heardat any of `the substations 'which mayatte-mpt to gainwaccess to the trunk,and the subscriber ivitl' thereby Ybe advised that the trunk line isin use.

vWhen the subscriber at A Vfrestoresthe rcceiverto its hook the associated relay R is deenergized, thus releasing the associated relay R and master relay 1R22, and th-us restoringall relays t0 normal, including relay R4, which results in the removal o'the busy tone fronrconductors 17 and 18; `The trunk is then free from any substation 'to appropriate it `for its exclusive use.

It Will'be evident thatby this limproved circuit arrangement any one of ainumber of substations may have exclusive use of a line leading to a central station lor :the like. BY the use of said arrangement l'means is also provided to inform any `other calling subscriber when theline 'is busy. In carrying out lthis invention a minimum of apparatus is utilized, and a resulting saving in current consumption is afforded it is desired `to secu-re 'by `Letters-Patent is:

1. In a telephone system, a plurality ot associated stations, la line for connecting-*said stations to a distant station, talking conductors for each station, relays associated with each of saidtalking conductors, relays controlled vbyeach of said irst mentioned vrelays, means controlled'b-ysaid second .mentioned relays v-vvhereby `exclusive connection 'may be established between anyone of the associated stations and distant` station, 'a 1retardatlon coil common fto said associated llO stations, and means whereby said retardation coil will be intermittently short circuited through one of its windings and abusy tone transmitted to any of the associated stations `associated stations, a line for connecting said stationstoa distant station, talking conductors for each of said stations, a relay associated with each of said talking conducto-rs, means whereby exclusive connection may be established between any one of said associated stations and the distant station, a retardation coil associated with said relays, and means whereby said retardation coil will be intermittently short circuited through one of its windings and a busytone transmitted to any of the associated stations upon an attempt to originate a call there-4 from while the line is in use.

3. In a telephone system, a plurality of associated stations, a line for connecting said stations to a distant station, talking conductors for each station, connection-changing relays individual to said stations, a second relay associated with each of said connection-changing relays, means adapted to associate any of said talking conductors with said line upon the energizationv of any of said connection-changing and second relays, a master relay common to said stations and responsive to the operation of an initial connection changing relay, said master relay having its winding connected in series with the winding of the actuated connection changing relay in the energizing circuit thereof, and means including said master relay whereby exclusive connection is established ywith said distant station upon the association of the talking conductors of that substation with said line.

4. In a telephone system, a plurality of associated stations, a line for connecting said stations to a .distant station, talking conductors for each station, a connectionechanging relay individual to said stations, a second relay associated with each of said connection varying relays, means adapted to associate any of said talking conductors with said line upon the energization ofany kof said connection-changing and seco-nd relays, a master relay common tosaid stations and responsive to the operation of an initial connection changing relay, said master rela having its winding connected inseries with the winding of the actuated connection changing relay in the 'energizing circuit thereof, means including said master relay whereby exclusiveconnection is established withsaid distant station upon the association of the talkingconductors of that substation with said line, and means whereby ya. busy' indicationwill be transmitted to any of the associated stations upon an attempt to .initiate a call therefrom while the line is in use.

5. In. a telephone system, a plurality of y 'e associated stations, a line .for connecting said stations to a` distant station, talking conductors for each station, a connectionchanging relay individual to said stations,v

a second relay associated with eachY of said connection-changing relays, means adapted to associate any of said talking conductors with said line upon the energization of any offsaid connection-changing andsecond relays, a master relay common to said stationsv ,Y '4

and responsive to the operation of an initial connection changing relay, said inaster relay having its winding connected in series with the winding of the actuated connection changing relay inthe energizing circuit thereof, means including saidl master. relay whereby thev other of said talking conductorsv are prevented from being simultaneo-usly associated with said,line,fan intermittently operable relay, a retardation coil associated therewith andfcommon to said associa-ted stations, and means including said intermittently operable relay and retardation coil whereby a busy indication will be transmitted to any of the associated stations upon an attemptto initiate a while the line is in use. y

In testimony whereof, we have signed our call therefrom names to this specification this 31st day of March, i919. f

YLEON D.v BARROWS.

LEO H. DARROW. 

